On Thu, 12 Oct 2017, David Coudert wrote:
Many authors avoid the empty graph (see e.g., the excellent book "Graph Theory with Applications" by Bondy and Murty) as there are no consensus on its properties. Should it be considered connected ? biconnected ? hamiltonian ? minor-free ? transitively reduced ?
True, and there has been a discussion about is_tree in this list. Anyways, different parts of Sage should use same definitions. -- Jori Mäntysalo
